The present invention relates generally to the field of electrical machines for energy conversion, such as motors and generators. Motors convert electricity into mechanical energy. Generators generate electricity by converting mechanical energy into electrical energy. A prime mover, such as an engine driving a rotating shaft, provides the mechanical energy. A rotor having permanent magnets or electromagnets rotates with the rotating shaft, generating a magnetic field that causes electricity to be generated in a stationary stator.
Superconducting electrical machines, such as a superconducting generator, use the principle of superconductivity to significantly reduce the electrical resistance in the conductors of the generator. Superconductivity requires maintaining the conductors at very low temperatures. However, such low temperatures relative to temperatures in an environment outside the superconducting electrical machine, such as a room temperature, lead to a large driving force for heat transfer into the superconducting electrical machine. Typically, complex and expensive sealing and vacuum pumping systems are necessary to maintain the conductors at very low temperatures. Expensive machines called cryocoolers are used to obtain superconducting coolant temperatures needed for superconductivity. Generally, one Watt of cooling load at superconducting temperatures may require about 100 Watts of power at room temperature.